1. Field of the Invention
The present invention is related to a bridge/router and a method for avoiding packet replication during a failure in a network. In one embodiment, the network is a video hub office which is associated with the distribution of IP television to homes.
2. Description of Related Art
The following abbreviations are herewith defined, at least some of which are referred to in the ensuing description of the prior art and the present invention.    BTV Broadcast Television    CO Central Office    DSL Digital Subscriber Line    DSLAM Digital Subscriber Line Access Multiplexer    FDB Forwarding Database    Gbps Giga-bits-per-second    IP Internet Protocol    MPLS Multi-Protocol Label Switching    PIM Protocol-Independent Multicast    RGW Residential Gateway    SAI Service Area Interface    SHE Super Headend    STB Set-Top Box    TV Television    VHO Video Hub Office    VoD Video-On-Demand    VRRP Virtual Router Redundancy Protocol
Referring to FIG. 1 (PRIOR ART), there is a block diagram that illustrates the basic components of an exemplary transport network 100 which can provide broadcast TV channels to homes via for example DSL phone lines. The exemplary transport network 100 shown includes two super head-ends 102, a backbone network 104, multiple VHOs 106, multiple IOs 108, multiple COs 110, multiple SAIs 112 and multiple RGWs 114. In operation, each super head-end 102 (which includes a router 116 and an acquisition server 117) receives international/national TV feeds and supplies those international/national TV feeds via the backbone network 104 to each VHO 106. Then, each VHO 106 (which includes an acquisition server 118, a first bridge/router 120a, a second bridge/router 120b, a first router 122a, a second router 122b and a VoD server 124) receives regional/local TV feeds and multicasts all of the TV feeds to their respective IOs 108. And, each IO 108 (which includes a router 126) then multicasts all of the TV feeds to their respective COs 110. Then, each CO 110 (which includes an bridge/router 128) multicasts all of the TV feeds to their respective SAIs 112. And, each SAI 112 (which includes a DSLAM 130) then sends a few TV feeds out of all the possible TV feeds to their respective RGWs 114 (which are associated with STBs 115). Thus, users can interface with their STB 115 and select one of the multicast TV channels to watch on their television set. The transport network 100 can also provide voice (telecommunications) and data (Internet) to the homes.
Referring to FIGS. 2A and 2B (PRIOR ART), there are two block diagrams illustrating the basic components within the traditional VHO 106 that has a data replication/bandwidth problem which will be solved by the present invention. In this example, the VHO 106 has an acquisition server 118 which is connected by two links 202a and 202b respectively to the first bridge/router 120a and the second bridge/router 120b. The first bridge/router 120a is connected by link 204 to the first router 122a. The second bridge/router 120b is connected by link 206 to the second router 122b. The first bridge/router 120a and the second bridge/router 120b are connected to one another via link 208. The first router 122a and the second router 122b are shown as being associated to one another via a VRRP 209 (which is a redundancy protocol that allows one or more routers (e.g., router 122b) to serve as standby/backup routers to a primary/master router (e.g., router 122a), and replace it automatically in case of failure; also, the group of redundant routers (e.g., routers 122a and 122b) are identified by a unique virtual IP address). And, the first bridge/router 120a, the second bridge/router 120b, the first router 122a and the second router 122b have a VPLS instance 210 (which is an emulation of Ethernet layer 2 network over IP/MPLS) operating between themselves. For a detailed discussion about VPLS, reference is made to the following drafts from the L2VPN working group of the IETF: draft-ietf-12vpn-requirements-07.txt, draft-ietf-12vpn-vpls-ldp-09.txt, draft-ietf-12vpn-vpls-bgp-08.txt (the contents of which are incorporated by reference herein). The VoD server 124 is not shown in these drawings or discussed herein since it is not relevant to the present invention.
In FIG. 2A (PRIOR ART), the VHO 106 is shown in a normal operating condition where the acquisition server 118 sends layer 3 IP multicast traffic 211 (e.g., TV feeds 211) to the first bridge/router 120a (e.g., VPLS edge bridge/router 120a). The first bridge/router 120a floods the received multicast IP traffic 211 on LSP_a towards the first router 122a (which is the PIM designated router 122a) and on LSP_b towards the second router 122b via the second bridge/router 120b (note: LSPs can be configured manually and the VPLS instance 210 automatically uses the LSPs to create pseudo-wires which are tunneled in the LSPs). This flooding results from the VPLS layer, which (as a bridge) replicates multicast traffic 211 to all outgoing ports because a multicast MAC address is never learned by a bridge source MAC learning function. In this situation, the LSP (and pseudo-wire) plays the role of a virtual L2 port for a VPLS virtual bridge. Again, this is the normal operating condition of the VHO 106 and there is no data replication/bandwidth problem.
In FIG. 2B (PRIOR ART), the VHO 106 is shown in a failed operating condition where there is a fault 212 on link 204 between the first bridge/router 120a and the first router 122a. The first bridge/router 120a implements MPLS so it knows about the fault 212 and in response it activates a backup LSP_a′ which carries the same IP multicast traffic 211 on links 206 and 208 via the second bridge/router 120b towards the second router 122b (which is now the PIM designated router 122b—why this is the case will be discussed in detail below). As can be seen, the first bridge/router 120a activates the backup LSP_a′ on the same port “p2” as the primary LSP_b and sends the same IP multicast traffic 211 to the second router 122b. This leads to packet replication on two links 206 and 208 which is unnecessary and wasteful. In addition, the physical links 206 and 208 (plus the other link 204) need to be over-dimensioned (e.g., from a 1 Gbps Ethernet link to a 10 Gbps Ethernet link—since there is no smaller increment with Ethernet links) to address this traffic replication/bandwidth problem. The over-dimensioned links 204, 206 and 208 result in increased costs. This traffic replication/bandwidth problem occurs in other architectures as well and is solved by the enhanced VPLS bridge/router and method of present invention.